1) Field of the Invention
The present invention relates generally to agricultural earthworking implements, and, more specifically, to a down pressure spring adjustment for a parallel linkage on an implement such as a row crop cultivator or the like.
2) Related Art
Implements such as row crop cultivators or planters often utilize a parallel linkage to connect a cultivator rig or planter assembly to a transverse tool bar or frame member. To bias the rig downwardly, coil springs may be tensioned diagonally between links. Some of the previously available rigs such as the type shown in U.S. Pat. No. 4,461,355 include a threaded adjustment to vary the tension of the springs and adjust the down pressure. Threaded adjustments typically require one or more tools to change the spring tension for the desired down pressure. Making adjustments to the down pressure for various rig tool combinations and ground and crop conditions can be very time consuming and difficult.
Some pressure adjusting systems for parallel linkages have structure for moving one end of the springs along one of the links. For example, a rack and pinion arrangement such as shown in U.S. Pat. No. 4,766,962 adjusts springs along the upper link of the parallel linkage to change spring tension and thereby adjust the down pressure. Such systems require a special retaining member which adds cost and complexity to the structure, and a separate tool is necessary to make pressure adjustments.
Most rig assemblies do not have a convenient or easily readable gauge or marking to determine the spring tension setting or provide repeatable settings. Often a time consuming trial and error method is necessary to set the down pressure on a large number of rigs so that the bias on each rig is approximately the same. With some pressure adjusting systems overtensioning is possible to the extent that stresses become greater than desired when the rig is in the working position.